Support for compensation aware data types in relational database systems

ABSTRACT

Techniques are provided for extending a business transaction framework to support user-provided compensation logic for business transactions. The extensibility framework may be used to implement user-defined semantics for (a) validating concurrent updates to shared data and (b) performing compensating actions when an associated transaction is aborted. In one embodiment, the extensibility and the compensation are provided at the data-type level. User-provided logic also maintains summaries that include values that are externalized so that they may be referenced in user-provided operational constraints.

PRIORITY CLAIM

The present application claims priority as a continuation of U.S. patentapplication Ser. No. 12/270,790, filed Nov. 13, 2008, entitled “SUPPORTFOR COMPENSATION AWARE DATA TYPES IN RELATIONAL DATABASE SYSTEMS”, whichclaims priority as a continuation-in-part of U.S. patent applicationSer. No. 12/102,831, filed Apr. 14, 2008, entitled “FRAMEWORK FORHANDLING BUSINESS TRANSACTIONS” (hereinafter the “BUSINESS TRANSACTIONAPPLICATION”), which claims priority to U.S. Provisional Application No.60/972,557, filed Sep. 14, 2007 entitled “FUNCTIONAL SPECIFICATION FORBUSINESS TRANSACTION, RDBMS, 11.2”. The entire contents of each of whichare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to extending a business transactionframework to support custom compensation rules.

BACKGROUND

In a traditional database system, the transaction management protocolsand mechanisms are constrained by the fundamental properties ofatomicity, consistency, isolation and durability (ACID). The transactionatomicity, which is the cornerstone of a transaction management system,states that a transaction either runs completely or has no effect on thesystem at all. The atomicity property indirectly impacts a transaction'sability to view the effects of another transaction while it is executing(visibility) and the database system's ability to recover in case of afailure (recoverability).

In a typical database system, a transaction's ability to view anothertransaction's uncommitted data is controlled using read locks ormulti-version read consistent views of data. Write locks protect atransaction's uncommitted data from being seen and modified by someother transaction. These write locks are held until the end of thetransaction and this is required to ensure that the system isrecoverable.

A transaction management system with strict ACID properties is effectivefor conventional database applications involving short execution times(short transactions) and relatively small number of concurrenttransactions (operating on the same data). However, it is excessivelyrestrictive for applications that involve reactive, long-lived, andcomplex transactions.

For example, a complex transaction may involve making the arrangementsfor a band's world tour. Such arrangements may involve booking manyflights, hotels, arranging car rentals, dining, etc. Completing all ofthe arrangements may take weeks. If the entire “world tour” transactionis modeled using a single database transaction, then certain records mayremain locked to other transactions for the entire duration. Forexample, a record that indicates how many seats are available on aparticular flight may remain locked (preventing other passengers frombooking seats on the same flight) until the “world tour” transactioneither commits or fails.

Keeping records locked for the duration of complex business transactionsis impractical and inefficient. However, if a complex businesstransaction is modeled using several independent database transactions,other problems may occur. For example, assume that a part of aparticular business transaction involves increasing the funds in anaccount. Further assume that the fund increase operation is performed asa distinct database transaction that is allowed to commit before theentire business transaction completes. After the fund increasetransaction commits, other transactions are able to see the increasedfunds in the account. One of those other transactions may be a“withdrawal” transaction that withdraws more funds from the account thanexisted in the account prior to the funds increase.

If the business transaction that performed the funds increase does notcomplete successfully, then it will be difficult to undo the changesmade by the partially-performed business transaction. In the currentexample, decreasing the funds of the account to undo the fund increasewill leave the account with a negative balance, due to the subsequentwithdrawal transaction. To avoid a negative balance, the withdrawaltransaction may have to be undone before the fund update transaction isundone. Undoing the withdrawal transaction may necessitate the rollbackof one or more additional transactions that relied on the changes madeby the withdrawal transaction. Situations like this, where aborting onetransaction may necessitate aborting one or more subsequenttransactions, are known as “cascading abort” situations.

The Business Transactions Application describes various techniques forfreeing up resources before the business transactions that change theresources have successfully completed. According to one embodimentdescribed therein, resources are freed up by committing databasetransactions that perform portions of operations before the operationsthemselves have successfully completed. If the operations fail tocomplete successfully, then “compensation information” is used to removethe effects of the committed changes that were performed as part of theoperation. The compensation information indicates the relative effect ofthe committed changes, so that the relative effect of the changes can beremoved without removing the effect of changes made to the resource bysubsequent transactions. Because the effect of changes made to theresource by subsequent transactions is not undone, application of thecompensation information does not result in a cascading abort situation.

The Business Transactions Application also describes various techniquesfor allowing database transactions to update values without retainingexclusive locks on those values. Consequently, even before a firsttransaction that changed a value commits, a second transaction isallowed to change the same value. If the first transaction fails tocommit, the effect of changes made by the first transaction are removedby applying compensation information. The application of thecompensation information removes only the effects of the changes of thefirst transaction.

As explained in the Business Transactions Application, a businesstransaction in the real world is often long lasting, discontinuous,distributed and is able to resume after a system failure. Examples forsuch business transactions include Travel Reservations, InventoryManagement and Provisioning. On the other hand, a database transactionin an RDBMS is typically short lived (to avoid deadlocks and issues withlow concurrency), completed within a single thread and is lost in thecase of a system failure (assuming the transaction did not commit beforethe failure). In the absence of a business transaction framework withina database system, business transaction logic is often implemented inthe application-tier outside the database system due to this mismatchbetween a business transaction and a database transaction.

When business transactions are implemented in the application tier, eachinteraction with an information system (database) is typically modeledusing a separate database transaction so that the locks on the modifiedresources are only held for the duration of the database transaction.Each business transaction has one or more database transactionsassociated with it. Even though the database transactions are committed,from the business transaction point-of-view, the operations performed onthe information systems are considered unconfirmed until the businesstransaction itself is committed.

Unlike traditional database transactions, which hold the write locks onsome modified data until the end of the transaction, a businesstransaction modeled in the application-tier relinquishes the locks muchbefore the end of the transaction. Hence, concurrent businesstransactions modify the common data while retaining the effects of otherunconfirmed business transactions. To support shared updates to commondata (with proper validation) applications often keep track of stateinformation pertaining to each on-going business transaction. When thebusiness transaction is aborted, the same state information is used togenerate meaningful compensating operations to undo the effects of aspecific transaction while keeping the other transactions intact. Thecompensation logic is application dependent and is often hand-coded tomeet business needs.

The Business Transaction Application describes a framework to managelong-running business transactions in the database. Under thisframework, the database server maintains the lifecycle of businesstransactions and the state pertaining to each business transaction. Theframework also supports commonly-used compensation mechanisms as dataclassification mechanisms—MEASURE and CATEGORY, and the ability toexpress the compatibility tests for concurrent operations on common dataitems as declarative operational constraints.

Unfortunately, the pre-built data classification mechanisms (MEASURE andCATEGORY) proposed by the Business Transaction framework may prove toorestrictive for a wide range of applications needing custom compensationlogic. If applications need compensation logic that does not match thepre-built data classification mechanisms provided by the businesstransaction framework, applications are forced to revert to usingdatabase transactions as surrogates for the business transactions, thustying up resources for extended durations, as described above.Alternatively, the business transaction logic may still be implementedin the application-tier. Such implementations are often plagued withinefficiencies and/or higher cost of management.

The approaches described in this section are approaches that could bepursued, but not necessarily approaches that have been previouslyconceived or pursued. Therefore, unless otherwise indicated, it shouldnot be assumed that any of the approaches described in this sectionqualify as prior art merely by virtue of their inclusion in thissection.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a flowchart illustrating steps performed on each updatedcolumn to determine whether the update is valid based on user-providedupdate-validation logic, according to an embodiment of the invention;

FIG. 2 is a flowchart illustrating steps for determining whetheroperational constraints are satisfied based on user-providedconstraint-checking logic, according to an embodiment of the invention;

FIG. 3 is a block diagram illustrating an extensible businesstransaction platform according to an embodiment of the invention; and

FIG. 4 is a block diagram of a computer system upon which embodiments ofthe invention may be implemented.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however,that the present invention may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form in order to avoid unnecessarily obscuring thepresent invention.

Functional Overview

Techniques are described herein for extending the business transactionframework (described in the Business Transaction Application) to supportuser-provided compensation logic for business transactions. Theextensibility framework described herein may be used to implementuser-defined semantics for (a) validating concurrent updates to shareddata and (b) performing compensating actions when an associatedtransaction is aborted. In one embodiment, the extensibility and thecompensation are provided at the data-type level.

Shared Updates

The Business Transaction Application introduced the concept of sharedupdates. Shared updates allow concurrent business transactions toperform updates to common data without holding exclusive locks on thedata for the duration of the business transactions.

A transaction's ability to perform shared updates is determined by thesemantics of the data being updated. For example, a field maintainingthe current capacity of a flight can be updated by concurrent businesstransactions as long as the resulting value (for all possible outcomesof the unconfirmed business transactions) is within the valid range.

The exact semantics that determine the shared update behavior for a datatype are 1) the ability to test the compatibility of each incomingUPDATE request with those that are already performed (and pending forconfirmation) on the same data instance and 2) the ability to undo aspecific UPDATE operation without reverting to cascading aborts. For theearlier example, if a modification to the capacity field is measured interms of the quantity of change (instead of absolute values before andafter the modification), a specific reservation request can be undone,with no impact on other concurrent operations, by simply negating thequantity of change.

The Abstract Data Classification Type

According to one embodiment, columns containing traditional databasedata types are made “compensation aware” by associating shared updatesemantics with the specific usages of that data type. For example,assume that the capacity column in a reservation table is configuredwith NUMBER data type. To allow escrow-like operations (simultaneousincrements and decrements by concurrent transactions) on this NUMBERcolumn, additional semantics are associated with the column using anextensibility framework. The shared update semantics for a data type canbe defined using the Business Transaction extensibility frameworkdescribed herein.

According to one embodiment, an abstract data classification (ADC) typewith specific methods for performing various businesstransaction-related operations is defined. According to one embodiment,the ADC type includes methods for:

-   -   validating an update operation in the presence of other        concurrent operations,    -   computing the compensated value for a specific UPDATE operation,        and    -   confirming the effects of an UPDATE operation.

Customized Data Classification Types

Because the ADC type is an abstract data type, the ADC type specifiesthe interface, but not the logic, for these methods. To support aparticular type of compensation, users create customized dataclassification (CDC) types by extending the ADC type and implementingits methods. Thus, the methods of CDC types containclassification-specific code to implement the logic for:

-   -   validating an update operation in the presence of other        concurrent operations,    -   computing the compensated value for a specific UPDATE operation,        and    -   confirming the effects of an UPDATE operation.

For example, a user may extend the ADC type to create a CDC type named“EscrowType” to support escrow-like shared update operations. TheEscrowType CDC type shall be used in various examples hereafter.However, EscrowType is merely one example of a CDC type that may becreated by users to implement customized compensation semantics. Thereis no limit to the compensation-type or semantics that a user mayimplement using the extensible framework described herein.

Attaching Compensation-Aware Semantics

Once a CDC type 302 has been defined by a user, the semantics of the CDCtype must be associated with the column(s) to which those semantics areto be applied. In one approach (referred to herein as the “attachmentapproach”), programmatic interfaces are provided to attach the semanticsof CDC types with columns that are defined as having a native data type(NUMBER, VARCHAR2 etc.). For example, consider the following code:

CREATE TABLE Flights (flightId NUMBER,  origDate DATE  currCapacityNUMBER); begin  dbms_btx.assign_su_semantics (table_name => ’Flights’, column_name => ’currCapacity’,  data_class =>  EscrowType( )); end;

In this code sample, the CREATE TABLE statement specifies the creationof a table “Flights” with three columns: flightID, origDate, andcurrCapacity. The flightID, origDate, and currCapacity columns areassociated with the native data types NUMBER, DATE, and NUMBER,respectively.

Before the dbms_btx.assign_su_semantics function is called, customizedcompensation semantics have not been attached to any of the columns ofthe Flights table. However, in response to the call to thedbms_btx.assign_su_semantics function, the database server attaches tothe column specified in the function call the semantics of the CDC typespecified in the function call. In this example, the database serverwould respond to the call to dbms_btx.assign_su_semantics by attachingto the currCapacity column of the Flights table the compensation-awaresemantics defined in the EscrowType CDC type.

Attaching compensation-aware semantics to columns in this manner allowsexisting applications to enable shared updates on the shared data withno data migration. Specifically, the compensation-aware semantics areattached without changing the underlying data type of the column (i.e.the data type of the currCapacity column continues to be NUMBER).

Encapsulating Compensation-Aware Semantics

Instead of or in addition to using the attachment approach, acompensation-aware data type can be modeled as an object type thatextends the base type with specific interfaces. In this approach(referred to herein as the “encapsulation approach”), the data for whichthe shared updates should be allowed is encapsulated within the dataclassification object type implementation, which is in turn inheritedfrom a base type.

For example, the EscrowType object type may include a generic capacityattribute, which stores the capacity for some resource. With thisapproach, the above Flights table may be defined as follows to allowshared updates on corresponding columns. The following code illustratesa call to create a Flight table in which the currCapacity column isdefined as an EscrowType column.

CREATE TABLE Flights (flightId NUMBER, origDate DATE,            currCapacity EscrowType);

Much of the discussion hereafter assumes that the attachment approach isused to establish a loose coupling between the table columns and thecorresponding data classification type. However, the concepts describedherein are applicable to both approaches.

Shared Updates with a CDC Type

Shared updates in the database are performed within the context of abusiness transaction. The Business Transaction framework maintains somemetadata for each shared update operation, which is in turn used tovalidate subsequent update requests to the same field, as well ascompensate for the original operation in case of the transaction abort.The exact metadata maintained for each update operation, and its usage(for validation and compensation), are user programmable with a specificimplementation of the ADC type.

A CDC type has an associated ADC type. The ADC type has specific methodsto perform maintenance operations for significant events in thelifecycle of a business transaction. The CDC type providesuser-customized logic for those methods. According to one embodiment,the ADC type has the following methods:

-   -   isValidChange    -   prepJournalRecord    -   confirmUpdate    -   abortUpdate    -   isSupportedDatatype

A new CDC type may be defined by extending the base ADC type andproviding logic for implementing these methods. Each of these methods,and the circumstances in which they are invoked by the BusinessTransaction framework, shall be described in greater detail hereafter.

The isValidChange Method

Once the mapping between a CDC type and a column is established, thebusiness transaction framework invokes the isValidChange method tovalidate an update operation that attempts to modify a value stored inthe corresponding compensation-aware column.

The isValidChange method has access to other concurrent changes to thesame value, and the implementer of the CDC type may rely on thisinformation to check if the current update operation is compatible withconcurrent (shared update) operations.

The prepJournalRecord Method

Upon successful validation of an Update operation (which could performchanges to multiple columns), the business transaction framework invokesthe prepJournalRecord method for each modified column to prepare thenecessary metadata for the shared update operation. The metadatareturned by the prepJournalRecord method is stored in the BusinessTransaction journal for subsequent operations.

The implementer of the CDC type can also maintain incremental summariesfor concurrent shared update operations to a specific value, and makethese summaries part of the metadata maintained in the BusinessTransaction journal. The summaries computed here are accessible in themethod validating the UPDATE operation (isValidChange method) as well asin the declarative operational constraints, which can performcross-column validations for each shared update operation.

The confirmUpdate Method

When a business transaction confirms, all the associated shared updateoperations are considered confirmed. The confirmUpdate method is invokedto perform some housekeeping operations on the journal, to adjust anysummaries maintained for the shared updates. The confirmUpdate methodallows application-specific journal maintenance operations at the timeof transaction confirmation.

The abortUpdate Method

The abortUpdate method is invoked by the framework for each sharedupdate operation associated with a business transaction that iscurrently aborting. The abortUpdate method, in addition to makingnecessary journal maintenance operations, computes the compensated valuefor the specific data modification that is being aborted and returnsthis value to the business transaction framework. The framework usesthese compensated values to make necessary changes to the table data.

The isSupportedDatatype Method

When a CDC type is associated with a table column to enable sharedupdates using the attachment approach, the type implementation and thetable column should agree on the data type for the values. For example,an EscrowType implementation is only applicable to columns of INTEGERdata type (and possibly FLOAT and DOUBLE data types). The BusinessTransaction framework enforces such restrictions by invoking theisSupportedDatatype method while associating the shared update semanticswith a specific table column.

Validating Update Operations

Using the framework and techniques described herein, the validation ofan UPDATE operation can be done in a variety of ways, including: 1)Programmatic approach with isValidChange method, and 2) Declarativeapproach with operational constraints.

As explained in the Business Transaction Application, operationalconstraints are conditional expressions that should evaluate to true forany update operation on a specific column to succeed. The operationalconstraints are expressed using multiple versions of data, namelycurrent, confirmed, and projected, for the impacted table row.

According to one embodiment, these values are accessed within theoperational constraints using pseudo variable extended column names. Forthe purpose of discussion, it shall be assumed that the pseudo variablenames for the current, confirmed and projected values are, respectively:btx_current.currCapacity, btx_confirmed.currCapacity, andbtx_projected.currCapacity.

An extensible data classification implementation maintains the confirmedand projected version for the corresponding data through all thebusiness transaction operations (with appropriate logic inprepJournalRecord, confirmUpdate, and abortUpdate methods). These valuescan be referenced in the operational constraints using extended names.

While the isValidChange method validates the update operation basedexclusively on the column data (current change, past changes to the samecolumn value, and any computed summaries), the operational constraintscan be used to enforce cross-column validations. For instance, whencurrCapacity and maxCapcity are two columns in the same table, anoperational constraint“btx_projected.currCapacity<btx_confirmed.maxCapacity” may be specifiedfor the currCapacity column, in which case, the validation for theupdate operation is based on a multi-column constraint.

Externalizing Summaries

According to one embodiment, summaries computed within a CDC type 302are externalized so that user-provided logic of the operationalconstraints may make reference to the summaries. In one embodiment, thesummaries are externalized using one or more operators configured withthe type. Each operator has a name, data type information, and a mappingto the entry in the journal.

For example, an EscrowType implementation may choose to compute (a) thesum of all value increments, and (b) the sum of all value decrements, assummaries. Under these circumstances, two operators BTX_ESCROW_INCR andBTX_ESCROW_DECR may be defined to externalize the summaries as numericaldata. With this configuration, an operational constraint may be definedas follows:

btx_current.currCapacity between (minCapacity+BTX_ESCROW_INCR(currCapacity)) and (maxCapacity+BTX_ESCROW_DECR (currCapacity))

The above operational constraint ensures that shared updates to thecurrCapacity column are allowed as long as all possible outcomes of theoutstanding business transaction leave the value within a range definedin the minCapacity and maxCapacity columns in the same row.

Mutable Updates

The projected version of a column value is the value that includes theeffects of all concurrent shared update operations on the data. In mostcases, this is also the value stored in the corresponding table column.For example, an Update operation on a column configured for Escrowsemantics changes the value stored in the column by a specific amountand also maintains the magnitude of change in the business transactionjournals. The projected value in this case is [confirmed value+sum ofall increments−sum of all decrements to the value], which is the actualvalue stored in the table column. But in some rare cases, the projectedvalue could be different from any value that is specifically set by anUpdate operation. For instance, a Multi-level security application mayuse a lattice structure to define the valid data transformation forshared update operations. Such a security application may stipulate, forexample, that the projected value for a set of operations is thesupremum of all the unconfirmed changes.

To allow such data classification methodologies, the extensibleframework described herein supports a mutable update option for theextensible type implementation. A mutable update option allows a newcomputed value to be written to the table column at the time of a sharedupdate. When this option is used, the prepJournalRecord method, whileprocessing an update operation initiated by the end user, may determinethat the value to be stored in the table column is different from thevalue set by the last operation and returns this new value to thebusiness transaction framework. The framework in turn overwrites thevalue set by the current update operation with the value returned by thecustom implementation.

The Business Transaction Journal

The Business Transaction framework maintains the journal information forall on-going shared update operations in a persistent table. Thisjournal information facilitates additional row specific (shared updatesto the same row by other transactions) and business transaction specificoperations (confirm or abort). In one embodiment, the journal table hasone entry for each column value that has at least one shared update by abusiness transaction. This entry summarizes the effect of all the sharedupdates to a specific value (nth column of mth row in a specific table)and it minimally has the confirmed and projected versions for the valuein encoded AnyData format. The AnyData format allows any SQL value, of anative type or a user-defined type, to be marshaled into AnyDatainstance and stored in a uniform structure. The journal entryadditionally stores any incremental summaries computed by theprepJournalRecord method for a specific data classificationimplementation.

In addition to the journal entry that summarizes the effects of allshared updates to a column value, each shared update operation on thevalue has a transaction-specific entry in the journal table. This too isreturned by the prepJournalRecord method and is used to performtransaction specific operations—make additional changes to the samevalue, confirm the transaction, and abort the transaction. Repeatedchanges to the same value within a single business transaction arecollapsed into a single transaction specific entry that captures thenet-effect of all the changes. For example, two separate Updateoperations within a business transaction may decrement the value in aspecific capacity column by two and then by three, resulting in ajournal entry that indicates that the transaction has decremented thecapacity by 5. In this example, the Escrow type implementation definedthe net-effect as the sum of all the current change and any past change.

The logic used for consolidating the requests is application dependent(and is programmed into the prepJournalRecord method). An alternateimplementation may choose to override the earlier request (fordecrementing the value by two) with the new request (decrement the valueby three). The prepJournalRecord implementation may also choose tomaintain summaries/effects for transaction-specific journal entries tofacilitate the net-effect computation.

Journal-Related Methods

In one embodiment, in addition to the methods described above, the ADCtype has a few static methods to provide secure access to the journalentries that may be relevant for extensible type implementations. Forexample, if a CDC type's shared update semantics rely on the order inwhich the concurrent Update operations are performed, then the journalentry for the operation that immediately precedes a specific operationcan be accessed using a getPrevJournalRecord method.

Other static methods available for journal maintenance operationsinclude getNextJournalRecord and deleteJournalRecord. ThedeleteJournalRecord method is applicable when the confirmation of aspecific update operation automatically invalidates other journalentries. For instance, for time-ordered compensation mechanism, in whicha last update operation that is confirmed prevails over all otherconcurrent changes, the deleteJournalRecord method may be used to deletethe journal entries corresponding to the operations that precede theupdate operation that is being confirmed.

Business Transaction Framework and CDC Type Interactions

FIGS. 1 and 2 are flowcharts that illustrate interactions between thebusiness transaction framework and the (Extensible) CDC types during anupdate operation, according to an embodiment of the invention. FIG. 3 isa block diagram illustrating a business transaction framework 306 andthe CDC types 302 that may be involved in that interaction. Asillustrated in FIG. 3, the CDC types 302 may be differentimplementations of the same abstract data classification type 300.

As explained above, a table enabled for business transactions may havedistinct data classification methodologies associated with each columnin the table. In general, during a standard update operation, whichmodifies a subset of the columns in the table, the corresponding CDCtypes 302 are used to validate the operation, as well as prepare thejournal entries.

Referring to FIG. 1, at step 100 the business transaction framework 306intercepts an Update operation on a table enabled for businesstransactions. For the purpose of discussion, the business transactionthat is attempting to make the intercepted update is referred to hereinas the “requesting business transaction”. This interception may beperformed in a variety of ways, including using a BEFORE ROW trigger, orwith an integrated kernel implementation.

In one embodiment, the update statements intercepted by the businesstransaction framework 306 employ standard SQL. Thus, databaseapplications that submit SQL against tables that have columns to whichCDC type semantics have been attached need not be modified to change thesyntax of the database commands that the applications send to thedatabase server.

Steps 102 to 116 define a loop that iterates over each column modifiedby the intercepted Update operation. At step 104, the businesstransaction framework 306 gathers the confirmed and projected versionsof the value that is being updated in the current column. In gatheringthis information, if the column value being updated has prior sharedupdates, the business transaction framework 306 loads the confirmedvalue and the projected value from the business transaction journals. Ifthis update is the first shared update operation to this specificcolumn, then the confirmed and projected values are set to thepre-update copy of the column value. As explained in the BusinessTransaction Application, the confirmed version of a value reflects allchanges made by confirmed business transactions, and does not reflectany changes made by unconfirmed business transactions. The projectedversion of the value, on the other hand, reflects changes made by othernot-yet-confirmed business transactions.

At step 106, the business transaction framework 306 determines whetherthe updating business transaction has previously updated the value inthe current column. If the updating business transaction has notpreviously updated the value in the current column, then control passesto step 110.

On the other hand, if the updating business transaction has previouslyupdated the value in the current column, then in step 108 the businesstransaction framework 306 invokes an undoChange method in the CDC type302 for the column being processed to undo the past changes by the sametransaction. The undoChange method adjusts the projected version of thecolumn, which now excludes the effects of past changes to the value madeby the requesting business transaction.

The effects of prior updates made by the updating business transactionare removed from the projected version at this point so that thevalidity determination may be made based on the net change that theupdating business transaction is attempting to make to the value in thecolumn. For example, if the updating business transaction previouslyreserved five seats on a flight, then released four seats on the flight,and is now attempting to reserve five more seats on the flight, then the“net change” of all changes made by the business transaction on theparticular value is reserving six seats.

Consequently, the validation determination should be based on whetherreserving six seats is permissible given the confirmed value of thecolumn and the possible outcomes resulting from changes on the columnmade by other, unconfirmed business transactions. Once the effects ofthe past changes of the updating business transaction have been undone,control passes to step 110.

At step 110, the business transaction framework 306 invokes theisValidChange method in the CDC type 302 to validate the current sharedupdate operation. All the necessary information (e.g. the confirmedvalue, the projected value, and the net change requested by therequesting transaction) is passed by the business transaction framework306 into the isValidChange method. If the isValidChange method returnsfalse, then control passes from step 112 to step 114, and the currentupdate operation is considered to conflict with other shared updateoperations and an error is raised. Otherwise, the business transactionframework 306 checks to see if there are any updated columns that havenot yet been processed 116.

If at step 116 there are any updated columns that have not yet beenprocessed, then control passes back to step 102, causing the nextupdated column to be processed. If all updated columns have beenprocessed and every call to isValidChange has returned TRUE, then,control passes to step 218 (shown in FIG. 2).

Referring to FIG. 2, at step 218 the business transaction framework 306uses the information loaded into the run-time state during steps 104-108to evaluate the operational constraints 304 (if any) associated with thecolumns being modified. As explained above, the operational constraints304 enforce cross-column dependencies to validate the shared updateoperation. If at least one operational constraint 304 fails, controlpasses to step 224 where an error is raised and the current updateoperation is restricted. As mentioned above, various operators such asBTX_ESCROW_INCR and BTX_ESCROW_DECR may be externalized so that usersmay construct declarative statements that reference values externalizedfrom the summaries.

If at step 218 no operational constraint fails, then at step 220 thebusiness transaction framework 306 invokes the prepJournalRecord methodfor each updated column, and makes/adjusts the journal entries based onthe values returned by the user-provided logic. At step 222, the sharedupdate operation is deemed compatible with other concurrent operationsand the update is successful.

Note that, in one embodiment, the database server already validatesintegrity constraints before the business transaction framework 306takes control in Step 100. So, violations with Uniqueness, Check (Notnull etc), and referential constraints are handled before the Step 100.

Business Transaction Confirm Operation

When a business transaction with one or more successful shared updatesis confirmed, the framework consults with the extensible implementationsand makes necessary changes to the journal entries. For example, in oneembodiment, the business transaction framework 306 ensures that theconfirmed versions for the values touched by the business transactionreflect the effects of confirming the transaction.

In one embodiment, in response to a confirm operation, the businesstransaction framework 306 invokes the confirmChange methods for all thecorresponding CDC types 302 to make use of the user-defined logic forcomputing the new confirmed value. The business transaction framework306 passes to the confirmChange method the information pertaining to thetransaction-specific journal entry, as well as the journal entrymaintaining the confirmed, projected and other summary values. Theimplementer of the CDC type 302 can make use of this information torecord the effects of current operation in its confirmed, projected andsummary values. The journal table is updated with these new values forthe summary journal entry and the transaction-specific journal entry isdeleted.

Business Transaction Abort Operation

When a business transaction is aborted, the effects of all the sharedupdates performed within the transaction should be undone. The processof undoing the effects of an aborted business transaction is called“compensation”. The implementer of the CDC type 302 determines the exactcompensation logic based on the semantics of the data, as well as othershared updates that are currently active in the system. The businesstransaction framework 306 invokes the undoChange method in the CDC type302 to get the user-computed compensated value, and makes necessarychanges to the dictionary and the base table to undo the effects of thetransaction.

The isValidChange Method and Operational Constraints

Operational constraints and the isValidChange Method serve similarpurposes. Specifically, both incorporate user-specified logic todetermine whether updates made by a business transaction should beallowed. However, isValidChange differs from operational constraints inthat the logic of an isValidChange implementation is specific to a CDCtype. The isValidChange logic is attached to a particular column byassigning the CDC type to the column. In contrast, an operationconstraint is defined on a per-column basis, and is not necessarilyassociated with any particular CDC type.

Because isValidChange implementations and operational constraints areboth mechanisms for determining whether updates made by businesstransactions are valid based on user-provided logic, in some situationsonly one or the other may be sufficient. Consequently, in oneembodiment, the isValidChange method is an “optional” method of a CDCtype. If operational constraints make all of the necessary checks todetermine whether an update by a business transaction is valid, then theuser need not implement the isValidChange method. If the user has notprovided an implementation of the isValidChange method, then theframework does not call the isValidChange method in step 108.

On the other hand, if all of the checking that needs to be done todetermine whether changes may be made to values in a particular columnis performed by the isValidChange implementation of the CDC typeassigned to the column, then the user need not define any operationalconstraints on the column. Under these circumstances, at step 208 inFIG. 2, there are no operational constraints for the businesstransaction framework to evaluate.

Pseudo Code for EscrowType Implementation

In the following sections, various pseudo code examples are given of howa user might actually design a CDC type 302 for use with the businesstransaction framework 306 described herein. However, it should be notedthat the syntax, operators, etc. used in these examples are merelyexemplary. The actual language, format, and syntax for defining a CDCtype 302 may vary from implementation to implementation.

For the purpose of illustration, the pseudo-code illustrates how a usermay specify the logic for an implementation of the EscrowType CDC type.The EscrowType is used to enable shared updates to a column storingnumerical data.

In the implementation depicted in the following pseudo-code, thenumerical data is assumed to be type casted into strings and passed inas arguments to the type implementation. Alternately, the numerical datamarshaled as AnyData instances can be passed in. This implementation canbe used to control shared updates to capacity columns by definingcross-column dependencies (e.g: maxCapacity column).

A missing isValidChange method from the specific type implementationindicates that type specific checks are always true, and the sharedupdates are validated using only operational constraints. The typeimplementation also externalizes the summary information computed withinthe type using two operators BTX_ESCROW_DECR and BTX_ESCROW_INCR.

create or replace type EscrowType extends btx$dataclass as  /** set theproperties for the extensible type implementation **/  member functiongetProperties return btxsys.btx$datacprop is  begin   -- create themapping between the summary maintained by the   -- the typeimplementation and the external operators --   returnbtxsys.btx$datacprop(       className => ‘Escrow ADC type’,      firstAuxOper => ‘btx_escrow_decr’,       firstOperTyp => ‘number’,      firstOperDfvl => ‘0’,       secondAuxOper => ‘btx_escorw_incr’,      secondOperTyp => ‘number’,       secondOperDfvl => ‘0’);  end; /** restrict the type to specific SQL data types for enabling **   **shared updates **/  member function isSupportedDatatype (           dataType VARCHAR2,            dataTypeOwner VARCHAR2) returnNUMBER is  begin    if (dataTypeOwner is null and      dataType in(‘INTEGER’, ‘NUMBER’, ‘FLOAT’)) then     return 1;    else     return 0;   end if;  end isSupportedDatatype;  /** prepare journal record basedon the information passed in **/  member procedure prepJournalRecord (            updValue IN OUT VARCHAR2,             updOptV1 IN OUTVARCHAR2,             updOptV2 IN OUT VARCHAR2,             confValue INVARCHAR2,             projValue IN OUT VARCHAR2,             auxOperV1IN OUT VARCHAR2,             auxOperV2 IN OUT VARCHAR2) is   chngNUMBER;  begin   chng := to_number(updValue)−to_number(projValue);   --the net change by the current operation is maintained   -- in theoptional value maintained for the individual   -- journal record --  updOptV1 := to_char(chng);   if (chng < 0) then    -- sum of alldecrements --    auxOperV1 := to_char(to_number(auxOperV1)−chng);   else   -- sum of all increments --    auxOperV2 :=to_char(to_number(auxOperV2)+chng);   end if;   projValue := updValue; end prepJournalRecord;  /** confirm a specific update to a value.Maintain the **   ** journal values to include the effects of tx confirm**/  member procedure confirmChange (             updIdent IN VARCHAR2,            updValue IN VARCHAR2,             updOptV1 IN VARCHAR2,            updOptV2 IN VARCHAR2,             confValue IN OUT VARCHAR2,            projValue IN OUT VARCHAR2,             auxOperV1 IN OUTVARCHAR2,             auxOperV2 IN OUT VARCHAR2) is   chng NUMBER; begin   chng := to_number(updOptV1); -- positive or negative --   --adjust the summaries maintained for the value --   if (chng < 0) then   auxOperV1 := to_char(to_number(auxOperV1)+chng);   else    auxOperV2:= to_char(to_number(auxOperV2)−chng);   end if;   -- confirmed valuewill be decremented if a negative   -- change and vice versa --  confValue := to_char(to_number(confValue)+chng);  end confirmChange; /** undo the specific update to a value. Maintain the **   ** journalentries accordingly **/  member procedure undoChange (            updIdent VARCHAR2,             compValue IN OUT VARCHAR2,            updOptV1 VARCHAR2,             updOptV2 VARCHAR2,            confValue VARCHAR2,             projValue IN OUT VARCHAR2,            auxOperV1 IN OUT VARCHAR2,             auxOperV2 IN OUTVARCHAR2) is   chng NUMBER := to_number(updOptV1);  begin   projValue :=to_char(to_number(projValue)−chng);   -- compensated value; value to beset for the base row --   compValue := projValue;   -- adjust thesummaries maintained for the value --   if (chng < 0) then    auxOperV1:= to_char(to_number(auxOperV1)+chng);   else    auxOperV2 :=to_char(to_number(auxOperV2)−chng);   end if;   -- confirmed value doesnot change when an operation is   -- aborted. --  end undoChange; endEscrowType;

Conclusion

Using the Business Transaction framework extensions described herein,existing database applications can be enabled for shared updates byassociating additional semantics to the columns in the table. Noapplication changes are required, as standard DML syntax is used tomanipulate the data stored in relational tables. Domain experts canimplement the shared update semantics for specific types of data, whichcan be plugged into the business transaction framework.

In addition, the levels of concurrency between update operations fromconcurrent transactions are determined using pre-programmed and/ordeclarative compatibility checks. The compatibility checks for sharedupdates are clearly divided into 1) those that have no externaldependencies and 2) those that need external dependencies. Thecompatibility checks that do not need external dependencies areimplemented as part of the extensible CDC type. The cross columncompatibility checks are made possible by externalizing summariescomputed by the CDC type. The extensibility framework allowsuser-defined data classification methodologies, which define the datasemantics and the compensation logic, to be plugged into the Businesstransaction framework.

Hardware Overview

FIG. 4 is a block diagram that illustrates a computer system 400 uponwhich an embodiment of the invention may be implemented. Computer system400 includes a bus 402 or other communication mechanism forcommunicating information, and a processor 404 coupled with bus 402 forprocessing information. Computer system 400 also includes a main memory406, such as a random access memory (RAM) or other dynamic storagedevice, coupled to bus 402 for storing information and instructions tobe executed by processor 404. Main memory 406 also may be used forstoring temporary variables or other intermediate information duringexecution of instructions to be executed by processor 404. Computersystem 400 further includes a read only memory (ROM) 408 or other staticstorage device coupled to bus 402 for storing static information andinstructions for processor 404. A storage device 410, such as a magneticdisk or optical disk, is provided and coupled to bus 402 for storinginformation and instructions.

Computer system 400 may be coupled via bus 402 to a display 412, such asa cathode ray tube (CRT), for displaying information to a computer user.An input device 414, including alphanumeric and other keys, is coupledto bus 402 for communicating information and command selections toprocessor 404. Another type of user input device is cursor control 416,such as a mouse, a trackball, or cursor direction keys for communicatingdirection information and command selections to processor 404 and forcontrolling cursor movement on display 412. This input device typicallyhas two degrees of freedom in two axes, a first axis (e.g., x) and asecond axis (e.g., y), that allows the device to specify positions in aplane.

The invention is related to the use of computer system 400 forimplementing the techniques described herein. According to oneembodiment of the invention, those techniques are performed by computersystem 400 in response to processor 404 executing one or more sequencesof one or more instructions contained in main memory 406. Suchinstructions may be read into main memory 406 from anothermachine-readable medium, such as storage device 410. Execution of thesequences of instructions contained in main memory 406 causes processor404 to perform the process steps described herein. In alternativeembodiments, hard-wired circuitry may be used in place of or incombination with software instructions to implement the invention. Thus,embodiments of the invention are not limited to any specific combinationof hardware circuitry and software.

The term “machine-readable medium” as used herein refers to any mediumthat participates in providing data that causes a machine to operationin a specific fashion. In an embodiment implemented using computersystem 400, various machine-readable media are involved, for example, inproviding instructions to processor 404 for execution. Such a medium maytake many forms, including but not limited to storage media andtransmission media. Storage media includes both non-volatile media andvolatile media. Non-volatile media includes, for example, optical ormagnetic disks, such as storage device 410. Volatile media includesdynamic memory, such as main memory 406. Transmission media includescoaxial cables, copper wire and fiber optics, including the wires thatcomprise bus 402. Transmission media can also take the form of acousticor light waves, such as those generated during radio-wave and infra-reddata communications. All such media must be tangible to enable theinstructions carried by the media to be detected by a physical mechanismthat reads the instructions into a machine.

Common forms of machine-readable media include, for example, a floppydisk, a flexible disk, hard disk, magnetic tape, or any other magneticmedium, a CD-ROM, any other optical medium, punchcards, papertape, anyother physical medium with patterns of holes, a RAM, a PROM, and EPROM,a FLASH-EPROM, any other memory chip or cartridge, a carrier wave asdescribed hereinafter, or any other medium from which a computer canread.

Various forms of machine-readable media may be involved in carrying oneor more sequences of one or more instructions to processor 404 forexecution. For example, the instructions may initially be carried on amagnetic disk of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system 400 canreceive the data on the telephone line and use an infra-red transmitterto convert the data to an infra-red signal. An infra-red detector canreceive the data carried in the infra-red signal and appropriatecircuitry can place the data on bus 402. Bus 402 carries the data tomain memory 406, from which processor 404 retrieves and executes theinstructions. The instructions received by main memory 406 mayoptionally be stored on storage device 410 either before or afterexecution by processor 404.

Computer system 400 also includes a communication interface 418 coupledto bus 402. Communication interface 418 provides a two-way datacommunication coupling to a network link 420 that is connected to alocal network 422. For example, communication interface 418 may be anintegrated services digital network (ISDN) card or a modem to provide adata communication connection to a corresponding type of telephone line.As another example, communication interface 418 may be a local areanetwork (LAN) card to provide a data communication connection to acompatible LAN. Wireless links may also be implemented. In any suchimplementation, communication interface 418 sends and receiveselectrical, electromagnetic or optical signals that carry digital datastreams representing various types of information.

Network link 420 typically provides data communication through one ormore networks to other data devices. For example, network link 420 mayprovide a connection through local network 422 to a host computer 424 orto data equipment operated by an Internet Service Provider (ISP) 426.ISP 426 in turn provides data communication services through the worldwide packet data communication network now commonly referred to as the“Internet” 428. Local network 422 and Internet 428 both use electrical,electromagnetic or optical signals that carry digital data streams. Thesignals through the various networks and the signals on network link 420and through communication interface 418, which carry the digital data toand from computer system 400, are exemplary forms of carrier wavestransporting the information.

Computer system 400 can send messages and receive data, includingprogram code, through the network(s), network link 420 and communicationinterface 418. In the Internet example, a server 430 might transmit arequested code for an application program through Internet 428, ISP 426,local network 422 and communication interface 418.

The received code may be executed by processor 404 as it is received,and/or stored in storage device 410, or other non-volatile storage forlater execution. In this manner, computer system 400 may obtainapplication code in the form of a carrier wave.

In the foregoing specification, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. Thus, the sole and exclusive indicatorof what is the invention, and is intended by the applicants to be theinvention, is the set of claims that issue from this application, in thespecific form in which such claims issue, including any subsequentcorrection. Any definitions expressly set forth herein for termscontained in such claims shall govern the meaning of such terms as usedin the claims. Hence, no limitation, element, property, feature,advantage or attribute that is not expressly recited in a claim shouldlimit the scope of such claim in any way. The specification and drawingsare, accordingly, to be regarded in an illustrative rather than arestrictive sense.

What is claimed is:
 1. A method for performing shared updates,comprising: receiving and storing user-provided logic for determiningwhether updates to a particular value in a particular column are validin the presence of concurrent updates to the particular value in theparticular column; receiving a request, associated with a particularbusiness transaction, to perform an update to the particular value inthe particular column; and in response to the request: (a) determining,for the particular column, a particular version of the particular value,wherein the particular version is one of: a projected version of theparticular value that reflects changes by at least one unconfirmedbusiness transaction different than the particular business transaction;or a confirmed version of the particular value that reflects changes byat least one confirmed business transaction different than theparticular business transaction; (b) causing the user-provided logic togenerate an indication of whether the update should be allowed, in thepresence of concurrent updates to the particular value in the particularcolumn, by: retrieving and invoking the user-provided logic, andpassing, to the user-provided logic, the particular version of theparticular value to enable the user-provided logic to determine, basedon the particular version of the particular value, whether allowing theupdate would violate one or more constraints on the particular column;wherein the one or more constraints on the particular column correspondto a conditional expression that, based at least in part on theparticular version of the particular value, evaluates to true when theupdate is valid; (c) determining whether to allow the update based, atleast in part, on the indication.
 2. The method of claim 1 wherein: thestep of receiving user-provided logic includes receiving animplementation of a method of a customized data classification type; andthe step of invoking the user-provided logic includes making a call tothe implementation of the method.
 3. The method of claim 1 wherein: thestep of receiving user-provided logic includes receiving a definition ofan operational constraint; and the step of invoking the user-providedlogic includes evaluating the operational constraint.
 4. The method ofclaim 3 wherein the operational constraint enforces cross-columndependencies.
 5. The method of claim 3 wherein the operationalconstraint references values externalized from summaries maintained bythird user-provided logic.
 6. The method of claim 1 further comprising,prior to invoking the user-provided logic, invoking second user-providedlogic to undo past changes to said value in the particular column thatwere made by the particular business transaction.
 7. The method of claim1 further comprising determining a net change based on all changes madeby the particular business transaction to said value of the particularcolumn.
 8. The method of claim 1 further comprising, in response todetermining that the update is allowed, performing the steps of:invoking second user-provided logic which prepares metadata for theupdate; and storing the metadata returned by the second user-providedlogic in a business transaction journal for subsequent operations. 9.The method of claim 1 further comprising: receiving an indication thatthe business transaction confirmed; and in response to the indication,invoking second user-provided logic to compute a new confirmed value forthe value; and storing the new confirmed value in a journal table. 10.The method of claim 1 further comprising: receiving an indication thatthe particular business transaction aborted; and in response to theindication, invoking second user-provided logic to obtain a compensatedvalue; and using the compensated value to undo effects of the particularbusiness transaction.
 11. The method of claim 1 wherein theuser-provided logic for determining whether updates to a particularcolumn are valid in the presence of concurrent updates to data items inthe particular column is encapsulated into an extensible data typeimplementation; wherein the extensible data type implementation isassociated with a field/column that receives shared update requests. 12.One or more non-transitory computer-readable media storing instructions,wherein the instructions include: instructions which, when executed byone or more hardware processors, cause receiving and storinguser-provided logic for determining whether updates to a particularvalue in a particular column are valid in the presence of concurrentupdates to the particular value in the particular column; instructionswhich, when executed by one or more hardware processors, cause receivinga request, associated with a particular business transaction, to performan update to the particular value in the particular column; andinstructions which, when executed by one or more hardware processors,cause in response to the request: (a) determining, for the particularcolumn, a particular version of the particular value, wherein theparticular version is one of: a projected version of the particularvalue that reflects changes by at least one unconfirmed businesstransaction different than the particular business transaction; or aconfirmed version of the particular value that reflects changes by atleast one confirmed business transaction different than the particularbusiness transaction; (b) causing the user-provided logic to generate anindication of whether the update should be allowed, in the presence ofconcurrent updates to the particular value in the particular column, by:retrieving and invoking the user-provided logic, and passing, to theuser-provided logic, the particular version of the particular value toenable the user-provided logic to determine, based on the particularversion of the particular value, whether allowing the update wouldviolate one or more constraints on the particular column; wherein theone or more constraints on the particular column correspond to aconditional expression that, based at least in part on the particularversion of the particular value, evaluates to true when the update isvalid; (c) determining whether to allow the update based, at least inpart, on the indication.
 13. The one or more non-transitorycomputer-readable media as recited in claim 12, wherein: instructionsfor receiving user-provided logic include instructions for receiving animplementation of a method of a customized data classification type; andinstructions for invoking the user-provided logic include instructionsfor making a call to the implementation of the method.
 14. The one ormore non-transitory computer-readable media of claim 12 wherein: theinstructions for receiving user-provided logic include instructions forreceiving a definition of an operational constraint; and theinstructions for invoking the user-provided logic include instructionsfor evaluating the operational constraint.
 15. The one or morenon-transitory computer-readable media of claim 14 wherein theoperational constraint enforces cross-column dependencies.
 16. The oneor more non-transitory computer-readable media of claim 14 wherein theoperational constraint references values externalized from summariesmaintained by third user-provided logic.
 17. The one or morenon-transitory computer-readable media of claim 12 wherein theinstructions further include: instructions which, when executed by oneor more hardware processors, cause prior to invoking the user-providedlogic, invoking second user-provided logic to undo past changes to saidvalue in the particular column that were made by the particular businesstransaction.
 18. The one or more non-transitory computer-readable mediaof claim 12 wherein the instructions further include: instructionswhich, when executed by one or more hardware processors, causedetermining a net change based on all changes made by the particularbusiness transaction to said value of the particular column.
 19. The oneor more non-transitory computer-readable media of claim 12 wherein theinstructions further include: instructions which, when executed by oneor more hardware processors, cause in response to determining that theupdate is allowed, performing the steps of: invoking seconduser-provided logic which prepares metadata for the update; and storingthe metadata returned by the second user-provided logic in a businesstransaction journal for subsequent operations.
 20. The one or morenon-transitory computer-readable media of claim 12 wherein theinstructions further include: instructions which, when executed by oneor more hardware processors, cause receiving an indication that thebusiness transaction confirmed; instructions which, when executed by oneor more hardware processors, cause in response to the indication,invoking second user-provided logic to compute a new confirmed value forthe value; and instructions which, when executed by one or more hardwareprocessors, cause storing the new confirmed value in a journal table.21. The one or more non-transitory computer-readable media of claim 12wherein the instructions further include: instructions which, whenexecuted by one or more hardware processors, cause receiving anindication that the particular business transaction aborted;instructions which, when executed by one or more hardware processors,cause in response to the indication, invoking second user-provided logicto obtain a compensated value; and instructions which, when executed byone or more hardware processors, cause using the compensated value toundo effects of the particular business transaction.
 22. The one or morenon-transitory computer-readable media of claim 12 wherein theuser-provided logic for determining whether updates to a particularcolumn are valid in the presence of concurrent updates to data items inthe particular column is encapsulated into an extensible data typeimplementation; wherein the extensible data type implementation isassociated with a field/column that receives shared update requests.